Embodiments of the invention relate to a powered system, such as a locomotive and/or an off-highway vehicle. Other embodiments relate to inverters and other power electronics in a powered system.
High current inverters employ high power gate turn-off devices (GTOs) when used with a traction motor, which switch in and out of conduction in response to gating signals from a system controller to invert a DC voltage to frequency-controlled AC voltage. One type of GTO that may be used is an insulated gate bipolar transistor (IGBT).
An IGBT combines the simple gate drive characteristics of MOSFETs with the high current and low saturation voltage capability of bipolar transistors. Plural IGBTs are usually used in combination. Hence, IGBTs have a lower on-state voltage drop with high blocking voltage capabilities in addition to fast switching speeds.
FIG. 1 depicts internal insulated gate bipolar transistors (IGBT) 12 that may be provided in an IGBT module 5. (“Module” refers to a discrete package having one or more solid-state devices, a housing or body covering the devices for protection and insulation purposes, and one or more leads that are electrically connected to the devices for accessing the devices external to the housing.) As illustrated, three IGBTs 12 are provided. Each IGBT 12 has a gate lead (G), a collector lead (C), and an emitter lead (E). Each gate lead (G), collector lead (C), and emitter lead (E) is available external the module 5 to be individually connected, as required for an intended function or operation. The IGBT module 5 depicted in FIG. 1 is used in a traction inverter. In the traction inverter, the gate leads (G) are connected in parallel. Though illustrated as being connected internally, the gate leads may also be connected externally.
A gate drive 22 also provided. The gate drive 22 is a switching element that is used to switch on and switch off the IGBT module. A primary function of the gate drive 22 is to convert logic level control signals into an appropriate voltage and current for efficient, reliable switching of the IGBT module 5. The gate drive 22 provides current and voltage of relatively precise values to assure that the IGBT module 5 is switched on and off, or gated into and out of conduction, at precise times. The gate drive 22 also provides for isolation of logic level control and fault feedback signals by having an isolated power supply associated with each gate drive. Gate drives are typically controlled by a processor. For illustration purposes only, the gate drive 22 shown schematically in the drawings is considered to include the processor and power supply. Operating conditions of the gate drive 22 and IGBT module 5 are monitored, specifically, parameters associated with the gate, emitter, and collector, to ensure an appropriate switching scheme for the IGBT module 5.
IGBT modules are currently used in traction inverters and auxiliary inverters associated with such powered systems as locomotives and off-highway vehicles. However, with respect to such powered systems, the same electrically rated IGBT module cannot be used economically in both traction inverters and auxiliary inverters. This is because auxiliary inverters require much less amperage than traction auxiliary inverters. Typically, traction IGBT modules have a current capability higher than double or triple that which is needed for an auxiliary inverter. Owners and operators of such powered systems would benefit from a system where a common IGBT module may be used in both traction inverters and auxiliary inverters.